Radiometric Dating: Making Sense of the Patterns

Radiometric dating methods sometimes yield conflicting results, but the technique itself is scientific and reliable, and once the results are interpreted in a biblical framework, they yield clear patterns that help us better understand the earth’s history since creation six thousand years ago.

Radiometric Dating 101

This three-part series will help you properly understand radiometric dating, the assumptions that lead to inaccurate dates, and the clues about what really happened in the past.

Part Two of this series showed that the same rocks can yield very different
ages, depending on which radiometric dating technique you use. These inconsistent
results are due to the problems of inheritance and contamination, which cause
the rocks’ chemistry to differ from the assumptions of standard radioactive
“clocks.”

Furthermore, new evidence indicates that radioactive elements in the rocks,
which are used to date the rocks, decayed at much faster rates during some past
event (or events) in the last 6,000 years. So the claimed ages of many millions
of years, which are based on today’s slow decay rates, are totally unreliable.

Does this mean we should throw out the radioactive clocks? Surprisingly, they
are useful!

The general principles of using radioisotopes to date rocks are sound; it’s
just that the assumptions have been wrong and led to exaggerated dates. While
the clocks cannot yield absolute dates for rocks, they can provide relative
ages that allow us to compare any two rock units and know which one formed first.

They also allow us to compare rock units in different areas of the world to
find which ones formed at the same time. Furthermore, if physicists examine
why the same rocks yield different dates, they may discover new clues about
the unusual behavior of radioactive elements during the past.

With the help of this growing body of information, creation geologists hope
to piece together a better understanding of the precise sequence of events in
earth’s history, from Creation Week to the Flood and beyond.

Different Dates for the Same Rocks

Usually geologists do not use all four main radioactive clocks to date a rock
unit. This is considered an unnecessary waste of time and money. After all,
if these clocks really do work, then they should all yield the same age for
a given rock unit. Sometimes though, using different parent radioisotopes to
date different samples (or minerals) from the same rock unit does yield different
ages, hinting that something is amiss.1

Recently, creationist researchers have utilized all four common radioactive
clocks to date the same samples from the same rock units.2 Among these were
four rock units far down in the Grand Canyon rock sequence (Figure 1), chosen
because they are well known and characterized. These were as follows:

Table 1 lists the dates obtained from each rock unit. Figure 6 (see below) graphically
illustrates the range in the supposed ages of these rock units, obtained by
utilizing all four radioactive clocks.

It is immediately apparent that the ages for each rock unit do not agree. Indeed,
in the Cardenas Basalt, for example, the samarium-neodymium age is three
times the potassium-argon age.

Nevertheless, the ages follow three obvious patterns. Two techniques (potassium-argon
age and rubidium-strontium) always yield younger ages than two other
techniques (uranium-lead and samarium-neodymium). Furthermore, the potassium-argon
ages are always younger than the rubidium-strontium ages. And often
the samarium-neodymium ages are younger than the uranium-lead ages.

What then do these patterns mean? All the radioactive clocks in each rock unit
should have started “ticking” at the same time, the instant that each rock unit
was formed. So how do we explain that they have each recorded different ages?

The answer is simple but profound. Each of the radioactive elements must have
decayed at different, faster rates in the past!

In the case of the Cardenas Basalt, while the potassium-argon clock ticked
through 516 million years, two other clocks ticked through 1,111 million years
and 1,588 million years. So if these clocks ticked at such different rates in
the past, not only are they inaccurate, but these rocks may not be millions
of years old!

Patterns in the Radiometric Ages: Figures 6 and 7. Click the picture to view a larger, pdf version.

But how could radioactive decay rates have been different in the past? Creationist
researchers don’t fully understand yet. However, the observed age patterns provide
clues. Potassium and rubidium decay radioactively by the process known as beta
(β) decay, whereas uranium and neodymium decay via alpha (α) decay (Figure
6). The former always gives younger ages. We see another pattern within
beta decay. Potassium today decays faster than rubidium and always gives younger
ages.

Both of these patterns suggest something happened in the past inside the nuclei
of these parent atoms to accelerate their decay. The decay rate varied based
on the stability or instability of the parent atoms. Research is continuing.

Relative Ages

Look again at Figure 1, which is a geologic diagram depicting the rock layers
in the walls of the Grand Canyon, along with the rock units deep in the inner
gorge along the Colorado River. This diagram shows that the radiometric dating
methods accurately show the top rock layer is younger than the layers beneath
it.

That’s logical because the sediment making up that layer was deposited on top
of, and therefore after, the layers below. So reading this diagram tells us
basic information about the time that rock layers and rock units were formed
relative to other layers.

Based on the radioactive clocks, we can conclude that these four rock units
deep in the gorge (Table 1) are all older in a relative sense than
the horizontal sedimentary layers in the Canyon walls. Conventionally the lowermost
or oldest of these horizontal sedimentary layers is labeled early to middle
Cambrian3 and thus regarded as about 510–520 million years old.4 All the rocks
below it are then labeled Precambrian and regarded as older than 542 million
years.

So accordingly all four dated rock units (Table 1) are also Precambrian.
And apart from the potassium-argon age for the Cardenas Basalt, all the radioactive
clocks have correctly shown that these four rock units were formed earlier than
Cambrian, so they are pre-Cambrian. (But the passage of time between these Precambrian
rock units and the horizontal sedimentary layers above them was a maximum of
about 1,700 years—the time between creation and the Flood—not millions of years.)

Similarly, in the relative sense the Brahma amphibolites and Elves Chasm Granodiorite
are older (by hours or days) than the Cardenas Basalt and Bass Rapids diabase
sill (Figure 1). Once again, the radioactive clocks have correctly
shown that those two rock units are older than the rock units above them.

Why then should we expect the radioactive clocks to yield relative ages that
follow a logical pattern? (Actually, younger sedimentary layers yield a similar
general pattern,5Figure 7.) The answer is again
simple but profound! The radioactive clocks in the rock units at the bottom
of the Grand Canyon, formed during Creation Week, have been ticking for longer
than the radioactive clocks in the younger sedimentary layers higher up in the
sequence that were formed later during the Flood.

Conclusion

Although it is a mistake to accept radioactive dates of millions of years,
the clocks can still be useful to us, in principle, to date the relative sequence
of rock formation during earth history.

The different clocks have ticked at different, faster rates in the past, so
the standard old ages are certainly not accurate, correct, or absolute. However,
because the radioactive clocks in rocks that formed early in earth history have
been ticking longer, they should generally yield older radioactive ages than
rock layers formed later.

So it is possible that relative radioactive ages of rocks, in addition to mineral
contents and other rock features, could be used to compare and correlate similar
rocks in other areas to find which ones formed at the same time during the events
detailed in Genesis, God’s eyewitness account of earth history.

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Answers Magazine

January – March 2010

Fossils are filled with mystery. They are commonly used to attack the biblical worldview, but in reality the Bible gives us the keys to help us solve these mysteries. How could recently discovered dinosaur tissue have survived until today? Why is the first fossil layer filled with such an astonishing variety of life (“the Cambrian Explosion”)? Read this issue to understand these and other mysteries of our world!

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